I always used Permatex Die-electric Grease, which is just a silicone grease. I'm guessing whoever used Gummi Pflege doesn't frequent the forum any more. Sounds promising.
Couldn't find any actual tests or comparisons. This was the closest thing I could find to a test:
https://www.bimmerforums.com/forum/showthread.php?1687676-Annoying-Door-Creaks-Gummi-Pflege-Test